Various types of ignition systems are known in which current flow through the primary of an ignition coil is controlled in such a manner that current flow is minimized, while maximum electromagnetic storage is obtained--see, for example, the referenced U.S. Pat. No. 4,176,645, to which German Patent No. 25 49 586 corresponds. In accordance with this disclosure, a signal representing a value, or parameter, which depends on the value of the current through the primary of the ignition coil, is obtained by passing the ignition coil primary current through a measuring resistor. The measuring resistor is serially connected with the primary winding and a switching path, that is, the main current carrying path of a control transistor. The primary current is high and, in order to safely pass the high primary current, the measuring resistor must be of substantial size, providing for good heat dissipation. Fitting such a resistor into an ignition system causes difficulties. The heating losses occurring in the measuring resistor waste energy.